Osteosarcoma of the distal radius is the most common type of bone tumor in dogs and affects over 10 000 dogs each year. To date, several surgical limb sparing techniques exist which result in functionally good outcome. Nevertheless, post-surgery complication rates with these techniques remain significant. Complications most commonly encountered include implant or bone failure, infection and tumor recurrence.
Limb sparing has been performed for over 25 years in dogs afflicted by primary bone tumors of the appendicular skeleton.1,2 Limb sparing consists in removing the segment of bone bearing the primary tumor and using internal or external fixation to the remaining bones with or without segmental bone replacement, resulting in a salvaged functional limb. Although amputation remains the standard of care to address the local tumor, some dogs are not good candidates for amputation because of concurrent orthopedic or neurologic disease or some owners are opposed to having an amputation performed. The prognosis for survival is the same with amputation of the limb or limb sparing.1,2 The anatomic sites most amendable to limb sparing are the distal aspect of the radius, the ulna distal to the interosseous ligament, and the scapula. The distal aspect of the ulna and the scapula are technically simpler because they do not require reconstruction3-6 and are not considered true limb sparing procedures by many for this reason.
The most common anatomic site where limb sparing is performed in dogs is the distal radius. Historically, the most commonly performed technique has been the use of an allograft7-11 to replace the critical bone defect created by segmental osseous excision. Although limb function is good to excellent in 75%-90% of dogs with the allograft technique,1,11 the complication rate is significant. The most common complications with this technique are infection, implant related problems, and local recurrence. Infection is reported in up to 70% of limbs,7 implant problems in up to 60%,7 and local recurrence in up to 60% as well.9 The allograft technique requires either the maintenance of a bone bank, which is time consuming and costly, or purchasing an allograft from a commercial site (https://vtsonline.com, for example) on a case by case basis.3 
Other surgical techniques have been developed for limb-sparing of the distal radial site. These techniques include: use of an endoprosthesis,11 distraction osteogenesis by bone transport,12,13 intraoperative extracorporeal radiotherapy,14 tumoral autograft pasteurization,15 microvascular ulnar autograft,16 ulnar rollover transposition,16,17 and lateral manus translation.18 Disadvantages of the bone transport osteogenesis procedure are the need for repeated multiple daily distractions of the apparatus and the significant amount of time required to fill the defect after tumor removal (up to 5 months).13 Microvascular autograft techniques require specialized equipment and training for the surgical team and add significant time to the procedure to allow microvascular anastomosis. Techniques that require the ipsilateral distal portion of the ulna to remain intact (ulnar rollover transposition and lateral manus translation) cannot be performed when the tumor invades the ulna.
The use of endoprosthesis carries the strong advantage of simplicity compared to the use of an allograft and consequently it is time-saving. The use of standard fixation plates bears limitations: they form a lap-type connection with the remaining bones, which is eccentric to the applied load, thus not offering an adequate support for the salvaged limb. Moreover, standard plates need contouring in the operation room to approach the natural curvature of the limb, thus extending the operation time.
Some of the above-mentioned problems are also present in other mammals, including other animals and humans.
Accordingly, there is a need in the industry to provide novel limb sparing techniques.